1. Field of the Invention
This invention relates to a method for reducing the adhesiveness of a water-soluble acrylamide-type polymer, and more specifically, provides a hydrogel of a water-soluble acrylamide-type polymer whose adhesiveness during drying to a pulverizable state is reduced so as to permit handling with good efficiency.
2. Description of the Prior Art
Water-soluble polymers such as polyacrylamide, a partially hydrolyzed product of polyacrylamide, and cationic, anionic or or nonionic copolymers containing acrylamide (to be generically referred to hereinbelow as acrylamide-type polymers) have recently gained increasing acceptance as paper strengthening agents, thickeners for use in paper-making and flocculating agents for treating water.
Various methods of polymerization, e.g., as described in Encyclopedia of Polymer Science and Technology, Vol. 1, (John Wiley and Sons, Inc. (1964)) and more specifically, methods such as aqueous solution polymerization (e.g., as described in U.S. Pat. No. 3,332,922), emulsion polymerization (e.g., as described in U.S. Pat. No. 3,284,393), suspension polymerization (e.g., as described in U.S. Pat. No. 2,982,749), radiation polymerization (e.g., as described in U.S. Pat. No. 3,477,932) or precipitation polymerization are known to prepare acrylamide-type polymers, but the aqueous solution polymerization method has been most widely used because it is economical and easily affords high-molecular weight polymers. From the stand point of economy in polymerization, transportation or drying, it is desirable to start the polymerization with a high monomer concentration.
As the concentration of the monomer increases, however, the resulting polymer becomes an elastomeric gel having a higher viscosity, and is difficult to handle as a fluid. A possible method for avoiding this difficulty would be one which comprises mincing such a high-viscosity elastomeric gel into coarse gel-particles, drying the particles using a rotary cylindrical dryer, a belt-type dryer or the like, and then finely pulverizing the dried particles thereby to produce a readily water-soluble powdery polymer that is easy to handle. This method, however, has the disadvantage that because of the adhesiveness of the polymeric gel, its adhesion to other substances or to itself becomes exceedingly high, and this is a great drawback in drying the polymeric hydrogel.
In order to solve this problem, U.S. Pat. No. 3,905,122 discloses a method which comprises extruding a high-viscosity elastomeric gel through a perforated plate, forming mutually adhering small gel globules by cutting the gel before or after passing the gel through the perforated plate, and drying the aggregate with hot air while applying a shearing force. This method is successful to some extent, and hydrogels of anionic or nonionic polymers can be treated relatively well with this method. Since, however, hydrogels of cationic polymers generally have a much higher adhesiveness than anionic or nonionic polymers, a reduction in the adhesion of the polymeric hydrogel particles to one another still cannot be achieved, and a good drying operation is difficult to perform.